Faced building element



Nov. 8, 1938'. K, TURK 2,135,544

EACED BUILDING ELEMENT Nov. 8., 1938.

K. TURK FAGED BUILDING ELEMENT Filed Aug. 3l 1935 Patented Nov. 8, 1938UNITED STATES PATENT OFFICE FACED BUILDING ELEMENT Baltimore, MarylandBaltimore, Md., a corporation of v Application August 31,-1936, SerialNo. 98,776

8 Claims.

The present invention relates to the production of a composite articlecomprising a metal base having permanently united therewith a relativelythin cellular porcelain enamel coating having a 5 roughened surfaceadapted to cause the composite article to readily adhereandbecome-united to any surface to which it is applied. The thin layer ofcellular porcelain enamel comprises the fusion product of porcelainenamel' material in the presence of a gas evolving agent, as hereinafterset forth.

It is desired to point out that said fusion product is of suiiicientthickness to function only as an adherence medium to cause the plate toadhere to the surface to which it is applied, all as hereinafter pointedout. I f

It is exceedingly diiiicult to cause metal sheets, such as sheet iron,or steel, or cast iron, to adhere to a given medium, as for example aWall hav- 20 ing a plaster or cement finish. It has previously beenproposed to weld tothe back of the metal ,sheet pins or lugs but thishas not proven satisfactory.- Further, considerable diiculty has beenexperienced in' the maintaining of metal sheets in position affixed tocement or plaster on external buildingvwalls, due to break-down of thebond between?. the through the forces of expansion and contraction, dueto temperature variations.

It is the primary object of the present invention'to provide a metalsheet which is incapable of adhering to many kinds of material, with arelatively` thin cellular lporcelain enamel coating provided withnon-connected cellular cavities having side walls of relatively greatrigidity capable of 'withstanding wide temperature variations, saidsurface providing means for causing the article to adhere to the surfaceto which it is applied.

It is an additional object of .the present invention' to provide asurface of the character above set forth in which the top surfaces ofthe side walls lie in slightly different planes, just sumcient toprovide a file-like surface.

It is a further object of the present invention tov provide articles ofthe character above set forth, one surface of which carries a decorativevitreous porcelain enamel. coating.

The roughened surface may be provided in a variety of ways, but it ispreferred that said surface be produced by removing the upper portion ofthe cellular backing, and thereby provide a multiplicity of cup-likedepressions greatly increasing the adhesive capacity of the cellularsurface. It is desired to point out that at least two plate and theplaster.

(c1. er1- 73) factors are involved in increasing the adherence of thesurface, the first being the increase of the surface area, and thesecond being the utilization of cup-like depressions which are used tokey the composite article when the same is forced against a cement orplaster surface, or the like.

One eld wherein the basic principles of the present` invention may applyis the architectural and building field. In the building eld, there is aWell defined trend'to finish the exterior and interior of building wallswith metal sheets carrying a vitreous coating of porcelain enamel. Thesemetal sheets are required to adhere to a building wall generallycomposed of ceramic fire-proofing brick or cement compositions. Thepresent invention provides means for causing the adherence of thesesheets which may carry on one surface a decorative vitreous coating ofporce- 4 lain enamel. Due to the fact that the porcelain sheetspreferably are enamelled on both sides to prevent warpage and distortionin processing, the enamel or ground coat makes it diicult to cause thesheets to adhere to the Walls unless some means are provided forincreasing the adherence capacity of the sheets. The invention will beset forth by reference to the accompanying drawings, wherein:

Figure 1'is a transverse section of the article before firing showingsomewhat diagrammati-- cally a metal base having on one of its surfacesa decorative vitreous coating, and on its reverse surface a ground coat,and thereover a coating of enamel adapted to form the adherent backingof the present invention.

Figure 2 shows the article after ring.

Figure 3 is a transverse section showing somewhat diagrammatically thered article provided K with the adherent coating from which the topsurface. or layer has been removed to provide a surface of greatlyincreased adhesive, adhering or gripping power.

Figure 4 is an enlarged cross section taken on line 4 4 of Figure 3.

Figure 5 is an enlarged cross section taken on line 5 5 of Fvigure 3. 45

Figure 6 is a transverse section showing somewhat diagrammatically thepresent invention applied to a semi-cylindrical metal plate having onits exterior surface a decorative vitreous coating and on its interiorsurface a ground coat, and 50 'thereover the adherent coating from whichthe top surface or layer has been removed to provide a surface ofgreatly increased adhesive, adhering or gripping power.

Figure is the reproduction of a photomlcro- `55 I ten times, whereinsaid cellular coating has been fired for two minutes at 1500 Fahrenheit.

Figure 8 is the reproduction. of a photomicrograph showing the cellularcoating magnied to ten times, wherein said cellular coating has beenfired for two and one-half minutes at 1450 Fahrenheit.

Figure 9 is the reproduction lof a photomicrograph showing the cellularcoating magnied t0 ten times, wherein said cellular coating has beenfired for four minutes at.1350 Fahrenheit.

It maybe noted that Figures 1 to 6 inclusive are not intended to beexact reproductions of an article according to this invention, but aremore or less diagrammatic. l

The 'process by which the articleI of the present invention is madecomprises applying to a base porcelain enamel .material havingincorporated therein a gas producing agent, ring the so-treated articleunder such conditions as to fuse or vitrlfy or semi-fuse orsemi-vitrifysaid material, and trap the gases evolving from thegas-producing agent, and then cooling the article. The porcelain enamelmaterial forms on the base, or where aground coat is used, lon theground coat, a relatively thin cellular layer of porcelain enamel fromwhich a top layer or lay-l ers may `be removed, preferably by grindingor other equivalent means, to give rise toa multiplicity of cup-likedepressions functioning to greatly increase the adhering and grippingqualities of the article. IThe preferred porcelain enamel material isporcelain enamel frit, although other porcelain enamel materials may beused.

Broadly stated; the metal sheetmay have on one side a fused porcelainenamel coating or any other vitreous enamel coating, -and there may bedirectly applied to the reverse side a porcelain enamel mixture whichhas incorporated therein a gas-producing agent, and the article may thenbe fired. Instead of applying the enamel material directly to thereverse side, a ground coat may be rst applied and then the enamelmixture having a gas-producing agent therein. The enamel on heatingbegins to fuse, and the gas evolves slowly, causing the enamel to risein a multitude of small bubbles much after the same fashion i'n whichordinary dough rises after baking powder or yeast has been added. Thisgives a ilnal product of cellular structure in which the volume has beengreatly increased and the specinc gravity has been greatly decreased.The bubbles range from `microscopic size upward, depending on thematerial added to the enamel and the subsequent treatment of the latter.

It is desired to point out that it is well known in porcelain enamels tointroduce materials such as, for example, iiuorides or organic materialscapable of being absorbed by clay to promote the formation ofsub-microscopic bubbles in the por'- celain enamel for the purpose ofincreasing opacity. These bubbles are not of sufficient size to produce,when the surface of the enamel is removed, cup-like depressions ofsufiicient depth to increase the adherence of the enamelled articletothe surface to which it lis applied. The bubbles of the presentinvention are of sumcient size so that when a surface is removed,cup-like depressions of sulcient deptharev produced to greatly increasethe adherence of the composite article to the surface to which it isapplied.

It is desired to point out that the porcelain enamel which may be usedto form the cellular backing is low in cost.- and can be easily appliedto the base member. No special enamel is necessary. In fact, it ispossible to use what is ordinarily considered scrap enamel, that isthrown away in the enameiing plant because of contaminationwith dirt oran admixture of enamels that would not combine oridnarily with oneanother. While this is the most economical source of the enamelmaterial, the consumption of enamel for this purpose will, undoubtedly,exceed th'e amount` of rejected enamel material on hand at any one time,and, therefore, probably it willbe necessary to mill up enamel for thisspecific purpose.

The following is an illustrative example of the present invention:Referring to Figure 1, a. sheet or article of `any other shape is firstcleaned by pickling, Sandblasting or other appropriate means, -to removescale and dirt. Thereafter, a coating or ordinary ground coat ofporcelain enamel H, such as is used every day in the enameling industry,is applied and fired on the sheet. This coating may be applied to one orboth ,faces of the sheet, depending upon the character of thesheet. If.steel sheets are used, it is customary to apply the ground coat to bothfaces of the sheet, to prevent warpage of the sheet. As well known tothose skilled in the art, the ground coat may be applied at the rate of36 grams per ,two square feet. Over the ground coat, on one side of thesheet, there is applied a fired decorative coat C, which may be coloredor plain. 'I'he reverse face of the sheet carrying the ground coat H hasapplied thereto, by spraying or otherwise, a cellular coating B,prepared as hereinafter set forth. The cellular coating B is appliedat arate of 40 to" 50 grams per square foot.

In most cases, it will be sufiicient to spray a single. coating of thecellular coating material B. The' coating, after being dried, is fired,the ring treatment being similar to that usual to porcelain enamel. Itmay be stated in general the higher the temperature of fusing the largerthe bubble size.

In preparing cellular material of the present invention, the choice ofenamel frits will be to a large extent governed by the' gas-producingmedia used, since the evolution of gases will be resultant either fromthe disintegration of said medium dueto thermal action or to thereaction of the medium with the enamel during fusion.

' The latter is the preferred type, since it is more readily controlled.The above reactions are of a thermo-chemical nature so that choice ofproper enamel frits for the present invention willrbe dependent not onlyupon the chemical composition of the frit but upon the fusiontemperature thereof. y For example, Formula No. 1, given below, isrepresentative of a type of frit which becomes fused orviscous, at atemperature of approximately 1500 F., while Formula No. 2 is.representative of a type of frit which fuses or becomes viscous at atemperature of approximately 1200 F. When cobaltous-cobaltic oxide(C0304) is fused into an enamel, it is taken into solution as cobaltousoxide (C00) with the liberation of one molecule of oxygen, the latter inthe form of a gas which is entrapped in the viscous enamel, causing itto swell. frit of Formula No. 1 is used at a temperature of 1500 F., thereaction takes place and swelling results. If, on the other hand,theenamel 'frit of Formula No. 2 is used mixed with cobaltouscobalticoxide, and heated to the fusion point of the enamel at 1200 F., thetemperature is not When the enamel 2,185,544 suiiicientto induce th'ereaction and no swelling results. Further, if calcium carbonate (CaCOa)yor.dolomite (Caf-MgCOs) be used with an enamel frit of the compositionshown in Formula No. 1,

.no chemical reaction will take place, even though the mixture be heatedto 1500.o F. On the other terial may be obtained by, heating to 1200 F.Other gas-forming materials, as for examples, Abarium carbonate (BaCOs)will give equally good results with either type of enamel frit.

FORMULA NO. 1 Typical enamel frit fusing at approximately Parts byweight Borax 26.0 Sodium nitrate 6.2 Fluorspar L 5.8 Cryolite 12.5 Flint15.3 Feldspar- 27.1 Zinc oxide 1.4 Potassium carbonate 1.0 Sodiumantimonate 4.1

FORMULA No. 2 Typical enamel ,frit fusing at approximately 1200 F. Y l

Parts by weight Feldspar 29.5 Sodium nitrate 4.1 Sodium carbonate 1.6Borax 25.4 Litharge 24.6 Zinc oxide 5.7 Cryolite 1.2 Fluorspar 5.7Antimony oxide 2.2

FORMULA No. 3

v Pounds Vitreous enamel frit (see Formula lNo. 1 for preparation offrit) Cobalt oxide (cobaltic-cobaltous oxide- C0304) 5 Nicke'lous oxide10 Water 35 lThe above mixture prior to .application to the metal'sheetis charged into a pebble mill and ground to a fineness of one gramresidue on a 325 mesh. screen from a 500 gram sample, wet weight. In thecase of the application of the enamel by slushing, it may be sometimenecessary to grind to a lesser ilneness in order to prevent cracking indrying. This flneness may be readily controlled by those skilled in theart. If the material tends to settle, a small amount of magnesiumsulphate or equivalent material is added to keep the material insuspension in the aqueous dispersion medium.

During the ring, th`e cobalt oxide reacts with the enamel frit as setforth above, releasing some ofits oxygen. 'I'he cobalt oxide being welldistributed in the porcelain enamel mixture, the oxygen evolvedtherefrom on heating is more or less evenly dispersed through the enamelmass, in the form of bubbles. lSince the size of the cuplike depressionsdepends uponl the bubble struc- 5 ture, it has been found that thedegree of adherence is influenced by the size of these cup-likedepressions. Thus, the smaller the size, .within limit, the greater thesurface 'area and the greater the adhesion will be. 10

Other vitreous enamel mixtures may be used withA equal success, withslight changes in the ring cycle. Such changes will .be obvious toanyone skilled in the art of porcelain enameling.

It will be readily understood by those skilled in 15 cthe art that theabove Formula. NO. 3 and the subsequent formulae given below, relate tothe preparation of the cellular material in aqueous suspension orso-called slip form.

'I'he following examples set forth wet milled 20 mixtures, which havegiven satisfactory results:

FORMULA No. 4

- Preferred Limits 25 Pounds Pounds vitreous enamel lrit (No. 2) 100Powdered dolomite (a natural calciummagnesum carbonate) 7% 5 to l5Vallendar clay 8 wam- 4o 30 FORMULA No. 5

Pounds Pounds Vitreous enamel frit (No. 2) 100 35 Calcium carbonate(OaC0;). 5 2% to l0 Water 30 FORMULA No. 6

`Pounds Pounds 40 Vitreous enamel frit No. 1 100 Barium carbonato 10 7%to 15 Bontonite 54 Water 35 FORMULA N o. 7 45 l Vitreous enamel [rit No.2-. Barium carbonate Bentonite ater FORMULA N o vitreous enemelfrit No. 1. Colaltous-cobaltic oxide- Admixtures of the above formulae havealso been found in some cases to lead to advantageous results, as thefollowing:

FORMULA No. 9

Vitreous enamel irit N o. 1 Cobaltous-cobaltic oxide Barium carbonateRmx fnn if Water..`

.Therefore it is not desired to be limited, in all cases, to this rangeof the gas-evolving agent.

The combination of materials and frits may be changed, the sequence ofsteps set forth need notv be followed and the temperature at which theenamel is fired mayv be changed, since with some gas producing agents,the bubbling or evolution of gas begins at quite a low temperature. Thegas producing agent .may be any of a number of insoluble organic orinorganic products, such as the various oxides, carbonates, sulphidesand other compounds which, at highers temperatures, release the water ofcrystallization or dissociate at a controllable rate.

As shown 1n Figures 3 and 5, the top surface or layer ofl the adherenceincreasing layer, after firing, is removed by an appropriate means, asby grinding off the top layer, to thereby expose the immediatelyadjacent surface F, the gripping area of which is greatly increased.

It is possible to remove the surface layer of the.

multi-cellular structure by an appropriate means.

While the usual base material is sheet or cast iron, other metals suchas stainless steel, copper, nickel, chromium or other plated steels andmetals may be utilized as the base member. Such a metal base may ormaynot carry a vitreous Acoating on the face opposite to that carrying thecellular insulating coating. For example.' the metal face may bechromium plated and the opposite base carry the cellular insulatingbacking. However, for the exterior of building walls, it is preferredthat the exterior face carry a vitreous coating, which may have adecorative effect, such effects being well known in the porcelain enamelart. The articles herein disclosed may also be used for the interiorwalls of buildings, and may be appliedy directly to the usual brown coatof plaster finish. The exposed face of'the metal base may have avitreous enamel coating, or may be chromium plated or otherwise,provided with a suitable finish.

It :will-be readily understood by those skilled in the art of porcelainenameling that the increased volume and decreased specific gravity ofthe cellular material as compared with the unfused vitreous enamelmaterial will be dependent upon the basic porcelain enamel used, uponthe type and amount of gas-forming medium andl upon the method ofapplication. Thus, for example, when the application is made byspraying, the increase in volume will be between six and eight timeswhile the specic gravity will be less than one-eighth of the original. t

,In some cases, it becomes possible to increase the volume to eighttimes, and similarly decrease the specific gravity to one-eighth of thespecific gravity of the unburned material. Since even greater increasein volume is possible by the proper combination of vitreous enamelmaterial and gas-forming material, it will be obvious to one skilled inthe art to decrease the specic gravity and increase zthe Volume to anydesired amount. Thercfore, it is notdesired to limit the invention tothe specic limit of extension set forth or the specific decrease in thespecific gravity set forth, but to claim any extension of u volume anddecrease in the specific gravity which may be tion. f

obtained by following the present inven- It is desired to point out thatthepreferred 'l gas-forming mediums are cobalt oxide, or a mixture ofcobalt4 and nickelous oxide, or barium carbonate, or a. mixture ofcobaltoxide and barium carbonate, or a mixture of -cobalt oxide, nickelousoxide as set forth, and barium carbonate. v

ffvhen the cobalt oxide is used' alone as a gasevoivingagent in a-mixture with porcelain enamel material, the preferred percentages arebetween 21A% to 7%, and when the barium carboriate is used alone, thepreferred percentages are between 10% and 15%.

When a mixture of nickelous oxide and cobalt oxide, as set forth, isused as the gas-evolving agent, the preferred percentages are 5% ofnickelous oxide and between 21/2% and 7% of cobalt oxide.

If cobalt oxide is used in a mixture with barium carbonate as 'thegas-evolving agent, the preferred percentages are from 2.1/2% to 51/2%of cobalt oxide, and from 5% to 10%lof barium carbonate.

If a mixture of nckelous oxide, barium carbonate and cobalt oxide isused as gas-evolving agent, thcpercentages are 5% nickelous oxide, 21/2%to 5% cobalt'oxide, and 5% to 10% barium4 carbonate. All of thepercentages are taken on the weight of Vthe vitreous enamel fritused`inthe mix.

Calcium carbonate is an example of an alkaline .earth carbonate. Whileit is preferred to use carbonates of this class, it isv desired to pointout that other metahcarbonates maybe used. Instead of using thecarbonates as the gas-evolving agent, in some cases, the alkaline earthsulphates may be used, such as barium, calcium, strontium sulphate.Other metal sulphates may also be used.

While it is preferredto use from 1/2% to 15% of the gas-evolving agent,in some cases, the limit maybe from 1/ to 20%.

In the form of the invention, as shown in Figure 6, there is provided acurved metal plate J, preferably in the form of a semi-cylinder, theouter surface of which carries a fired decorative coating of porcelainenamel K, the usual ground coat L being also provided. The interiorsurface of the plate carries a ground coat M and a celluiar coating N,provided with cells O. Units of this particular shape may be used toencase columns as for example concrete coated iron columns or concretecolumns.

Figure '7 is a reproduction of a photomicrograph, showing the cellularcoating magnified to lten times.

The cellular coating set forth in Figure 7 was produced by spraying,onto the ground,` coat enamel an adherence-promoting enamel compoundedin accordance with the herein disclosed gauge steel sheet which hadalready been provided with a fired ground coating having a thickvness ofapproximately 1.25 mm. The material which produces the cellular coatingon firing was applied to the fired ground coating at a rate of 48 gramsper square foot. The cellular coating was red for 2 minutes at i500Fahrenheit.

of the characteristics of the present invention that after the cellularmaterial is cooled there is I 4After firing, the material was cooled. Itis one A changes in temperature.

When reference is made to sidewalls of great rigidity, this is to beconstrued to refer to sidewalls of at least such strength and rigidityand of sufllcient thickness to hold the article to the applied' surfaceunder the stress induced by In other words, in certain localities it isnothing unusual for the temperature to vary from thirty to forty degreesin a single day. This gives rise to stresses, which must be resisted bythe walls of the-cells of the cellular coating. The side walls may, ofcourse,

have greater strength and rigidity "than aboveset forth.

Referring to Figure 7, the cells l having sidewalls 2 are approximatelyof the .same size. While there is some variation in the size of thecells, considering the entire cell surface the generalization may bemade that the cells are the same size and are approximately of the samedepth. In general, the maximum diameter of the cells, considering eachcell as a sphere, is ,about 2 mm. but may extend from 11/2` to 3 mm.While a3 mm. cell is twice the diameter of the 11/2 mm. cell, yet forthe purposes of the present invention thesecells can, because of thesmallness of the diameters involved, be considered cells ofapproximately the same diameter or nearly the same diameter. In otherwords, there is not a wide variation in the diameters of the cells. Thisuniformity of bubble size cannot, so far as the inventor is aware, beattained by any other method except by the method herein' set forth ofutilizing a viscous enamel with a gas-evolving agent, and trapping thegas-evolving agent in the viscous enamel, while regulating the timeand/or `temperature of ring, as hereinafter set forth.

These are relatively large cells, and as the cells` increase in size dueto control conditions, as hereinafter explained, there is some variationin `thev size of the different cells, one cell having a `of the cell isalso controlled by the amount of the material which is removed from eachcell. In other words, in the present case, considering the top row ofcells extending across the face of thearticle, at least the upper halfof the cell has been removed.

It is to be noted that thesidewalls too are not of the same height, orstated differently, the tops of the sidewalls are not in the same plane.This produces what may be termed a file-like surface. In other words,the same kind of surface is produced as is produced on a le, thatis, arough surface. This rough, file-like surface promotes the adherence ofthe cellular surface to the medium to which it is applied, and is afeature of the present invention. v Itis to be noted that the cells lpreferably extend down and just into theA upper surface of the groundcoat. A twenty gauge steel plate has a thickness of .9. mm. When groundcoat is applied on either side ofthe plate, the thickness of the platewith the two ground coats is 1.15 mm. This gives a thicknessof theground coat at about .125 mm. This yis an average thickness. With arather heavy gauge steel plate, the thickness of the ground coat mightbe increased, but this would be rather extra-ordinary. The cellularcoating, which is attached to the ground coating, after having its toplayer removed had a depth ofl .5 mm. making a total depth of the steelsheet with the ground coat on both sides and the adherent coating 1.65mm. An adherent coating of .5 mm. illustrates the type of adheringcoating which is the subject matter of the present invention. This maybe termed a relatively thin layer of cellular porcelain 'enamel which isprovided'with non-connected cellular cavities. It is recognized thatthis layer maybe increased and it may vary between .5 mm.' or lower and2 mm. For the purposes 'of the present invention, ran adherent coatingof 2 mm. would be arather thick coating. While it is not desired to belimited to any specific thickness of adherent coating functioning as anadhesive medium, it may be stated in general that the coating should, ingeneral, be between .5 mm. or lower and 2.0 mm. It is recognized,however, that the thickness of the coating may be somewhat greater.'I'he whole point is that all that is necessary is an extremely thinadherent coating, since the function of the coating is to act as anadhesive medium.

As shown in Figure 8, the cells 3 provided with sidewalls 4 are ofmuchsmaller diameter, but the depth is about'the same. The same enamelmixture No. 3 was used in making the cellular surface and, in general,the cells portrayed in Figure 8 were made under the very samecircumstances as that set forth in Figure '7, and all the remarks inFigure 7 made with reference to the production ofthe sample portrayed inFigure 7, are applicable to the sample portrayed in Figure 8, with theexception that the enamel forming the cells of Figure 8 was fired at avtemperature of 1450 Fahrenheit for two and onehalf minutes. Thisillustrates the step of controlling the size of the cells`or cup-likedepressions,by ring at a higher temperature. In other words, allconditions being the same, the higher the temperature of ring, thelarger the diameter of the cells, considering each cell as a sphere. Thetime of ring, as a usual thing, is increased with the decrease intemperature. This treatment is necessitated in order that the productmay be brought to complete vitriflcation and thus gain its maximumstrength and rigidity. The variation of firing time must be carefullycontrolled, in order to give the proper degree of vitrication, while atthe same time avoiding a decreased viscosity and an increase in bubblesize. Thus, the sample portrayed in Figure 'l was fired at 1500aFahrenheit for 2 minutes, and when the temperature was reduced fifty(50) degrees the time of ring was increasedl 1/2 minute. However, it isthe increase in temperature which is primarily responsible for theincrease in the size of the bubbles. In otherv words, as the temperaturegoes up the gas that is present in the viscous mix expands to produce alarger bubble. In carrying out the invention, the mix isheated so as totrap the major portion of the gases generated' by the gasevolving agent.'I'he cells 3 portrayed in Figure -8 have a diameter of about 1.5 mm.

eral, it is pointed out that the finer the cells the greater the keyingarea ofthe adhesive surface. The bubble size setforth in connection withthe discussion of Figures Z to 9 inclusive is illus- \trativeand thepresent invention is not limited to the formation of cells having thediameter and depths above set forth. Great variations can be made inthese and the resulting surface still comes within the spirit of thepresent invention. It is desired to point out that the bottoms of thecells are vitrified or semi-vitried and the sidewalls of the cells arepreferably cellular, while simultaneously being rigid and of highstrength. l

It is not necessary that the cells I, 3 and. 6 be embedded directly inthe ground coat. In fact, in'most cases said cells are underlain by alayer or layers of' cells of greatly reduced'diameter, which liedirectly on the ground coat, but it is preferred that thecells,'portions of which have been cut away and which expose cup-likedepressions, be fairly near to the ground coat, as this favors a strongadherence of this layer to the ground coat and therefore of the layer tothe metal-plate. It must bepointed out, however, that it is possible toremove the surface layers of the cellular material clear down to thelayer of cells immediately over the ground coat. While this gives asmaller cell size than cells, it has also been noted that the cells atthe bottom layer are more widely distributed,

that isjthe cell walls are thicker, so that the s'urface ar'ea at thispoint is not in .proportion to the diameter of the cells. It is to bepointed out that the size of the cells in anyone cellular layer, whilevarying from those in other cellular layers, will be substantiallyuniform and thus it may be possible to obtain various cell sizes for anyone composition and burning treatment, depending upon the depth 'ofthe'cellular.

material removed from the surface.' In general, however, this method isnot to be recommended. For the preferred form, the cellular surfacematerial is removed to a depth sufilcient to leave only two or threelayers of cells remaining above the ground coat.

While it has been stated that the surface produced in accordance withthe present invention may be used to key a metal plate, preferably asteel metal plate, to plaster, concrete or cement,

it is obvious that the cell-like porcelain enamel surfaces of thepresent invention may be keyed onto a mastic surface, asphalt surface orin fact to any kind of an intermediate surface that is plastic enough toreceive a roughened porcelain surface. y l

. The plates carrying the roughened porcelain surface may be of anysize. The present invention 'may be used to apply a cellular backing ofthe type herein-specified on tile, shingles, spanldrels, strips, panelsand in general for the usual building elements.

The present application is a continuation-inpart of application, SerialNo. 56,565, said prior application having matured into Patent No.'

I claim:

1. A composite article adapted to adhere to an applied surface,comprising a metal base provided with a fired ground coat and havingpermanently united therewith a relatively thin layer of the completelyvitried cellular -fushion product of porcelain enamel material in thepresence of 'a gas-evolving agent, the top portion `of said cellularlayer being removed to provide a'layer of nonconnected cellular cavitiesaffording large gripping surface, the thickness of said final cellularlayer varying between .5 mm. or lower and 2.0 A

mm., said cellular cavities having sidewalls of relatively greatrigidity capable of withstanding when in contact with the appliedsurface wide temperature variations.

2. A composite article adapted to adhere to an applied surface,comprising a metal base provided with a fired ground coat and havingpermanently united therewith a relatively thin layer of the completelyvitried cellular fusion product of 4porcelain enamel material in thepresence of a cobalt oxide gas-evolving agent, the top portion of saidcellular layer being removed to provide a layer of non-connectedcellular cavities affording large gripping surface, the thickness ofsaid final cellular layer varying 'between .5 mm. or lower and 2.0 mm.,said cellular cavities .having sidewalls of relatively great rigiditycapable of withstanding when in contact with the applied surface widetemperature variations.

3. A composite article adaptedto adhere to an applied surface,comprising a metal base pro- .vided with a fired ground coat and havingpermanently united therewith a relatively thin layer of the completelyvitriied cellular fusion product of porcelain enamel material in thepresence of a gas-evolving agent, the top portion of said cellular layerbeing removed to provide a layer of non-connected cellular cavitiesaffording large gripping surface, the thickness of -said nal cellularlayer varying between .5 mm. or lower and 2.0 mm., said cellularcavities having sidewalls of relatively great rigidity capable ofwithstanding when in contact with the applied surface wide temperaturevariations, the top surfaces of said sidewalls lying in slightlydifferent planes, providi'ng a4 file-like surface.

4. A composite article adapted to adhere to an applied surface,comprising a metal base provided with a fired ground coat and havingpermanently united therewith a relatively thin layer of the completelyvitried cellular fusion product of porcelain enamel material in thepresence or lower and 2.0-mm., said cellular cavities having sidewallsof relatively great rigidity capable of withstanding when in contactwith the applied surface wide temperature variations, the top surfacesof said sidewalls lying in slightly different Y planes, providing aille-like surface.

5. A composite article adapted to adhere to an applied surface,comprising a metal base provided with a fired ground coat and havingperplanes, providing a le-llke surface.

6. A composite article base proground coat and having permanently unitedtherewith a relatively thin layadapted to adhere to an -applied surface,comprising a metal vided with non-connected cellular cavities af#

